From owner-freebsd-hackers@FreeBSD.ORG Mon Aug 29 19:07:55 2005 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1D66916A41F for ; Mon, 29 Aug 2005 19:07:55 +0000 (GMT) (envelope-from samuel.pierson@gmail.com) Received: from wproxy.gmail.com (wproxy.gmail.com [64.233.184.194]) by mx1.FreeBSD.org (Postfix) with ESMTP id D621743D70 for ; Mon, 29 Aug 2005 19:07:47 +0000 (GMT) (envelope-from samuel.pierson@gmail.com) Received: by wproxy.gmail.com with SMTP id i30so809993wra for ; Mon, 29 Aug 2005 12:07:46 -0700 (PDT) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:mime-version:content-type:content-transfer-encoding:content-disposition; b=pXW09k+adyKGFdZSspM90z6e8/BGQPN4qUjoI4eYuolNe9el1+v1A6qEqMJzDUtYHkQSEs82Aiiq7keBNzb9TC62aLgyz1nU0twiNenD3mPrQff//q5d3CBkzO4x4j9kv48iZH9gjxqL6doGVJBrQwOu9H8qHCKxO2Xuwc2dk/4= Received: by 10.54.18.28 with SMTP id 28mr6523033wrr; Mon, 29 Aug 2005 12:07:46 -0700 (PDT) Received: by 10.54.144.1 with HTTP; Mon, 29 Aug 2005 12:07:46 -0700 (PDT) Message-ID: Date: Mon, 29 Aug 2005 14:07:46 -0500 From: Sam Pierson To: FreeBSD Hackers Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Subject: Atheros driver and radiotap reliability X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 29 Aug 2005 19:07:55 -0000 Hi guys, I'm trying to get an accurate measurement of signal strength (preferably=20 in dBm) on a per-packet basis between two atheros cards that I have. I had some correspondence with the ethereal developers and David Young and apparently there is a bug in how ethereal handles the radiotap header. David told me that tcpdump will correctly report whatever the device driver tells it is the correct signal signal strength, but not to trust it until t= he devices have been calibrated. How does the ath driver report the signal strength in the radiotap header? From tcpdump, it's giving me this value: /* taken from /sys/net80211/ieee80211_radiotap.h */ * IEEE80211_RADIOTAP_DB_ANTSIGNAL u_int8_t decibel (dB) * * RF signal power at the antenna, decibel difference from an * arbitrary, fixed reference. ... In this same file, there is a u_int8_t ANTSIGNAL reported in dBm. It appea= rs as though everything is driver (and device, probably) dependent, so I'd lik= e to know how the driver computes this value. =20 As a side question, does anyone have an easier way to reliably measure=20 per-packet signal strength? The area has a decent amount of traffic and= =20 I have to be able to analyze the packets themselves, so a plain hardware solution will not do. Thanks, Sam